One of the efforts for the third generation partnership project (3GPP) long term evolution (LTE) program is to bring new technology, new architecture and new methods into the new LTE settings and configurations. The LTE program is undertaken in order to provide improved spectral efficiency, reduced latency, and better utilization of radio resources, thereby providing faster user experiences and richer applications and services with less associated cost.
The objective of the evolved universal terrestrial radio access (E-UTRA) and universal terrestrial radio access network (UTRAN) is to develop a radio access network geared toward a high-data-rate, low-latency, packet-optimized system having improved system capacity and coverage. In order to achieve this, an evolution of the radio interface as well as the radio network architecture may be needed. For example, instead of using the code division multiple access (CDMA) air interface technology, such as is currently used in 3GPP, orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) may be used in the downlink (DL) and uplink (UL) transmissions, respectively. In addition, LTE may employ an all packet switched service, which would mean that all voice calls would be made on a packet switched basis.
In a scenario where radio resources are limited, high priority services, such as video conferencing, may attempt to acquire as much available radio resources as possible from those assigned to a wireless transmit/receive unit (WTRU). Since the network (NW) does not have any control over how granted resources are shared between applications, this may cause lower priority flows, such as hyper text transfer protocol (HTTP) flows, to be starved when a higher priority flow scales up to the available bandwidth.
In high speed uplink packet access (HSUPA), enhanced UL was built on the existing quality of service (QoS) model. In this model, when the network grants a radio resource to a WTRU, the WTRU is responsible for selecting which uplink QoS flow to serve, using the associated priority for each flow provided by the radio resource control (RRC) signalling. In this scheme, for the network to avoid resource starvation of lower priority flows, it may be required to provide those flows the same priority as the higher priority flows. However, by essentially aggregating these flows together, the WTRU assigns each flow equal transmission rights to each queue.
There are two proposals to solve UL starvation problem in radio access network 2 (RAN2). One is an NW centric solution and the other one is a WTRU centric solution. The NW centric solution is characterized by post-transmission traffic policing that is done by the NW after it receives data from the WTRU. No guaranteed bit rate (GBR), maximum bit rate (MBR) and prioritized bit rate (PBR) information should be transmitted to the WTRU.
A WTRU centric solution may include the pre-transmission of traffic policing. The traffic policing is performed by the WTRU before data is transmitted over the air, and the GBR, MBR and PBR information may be transmitted to the WTRU at radio bearer (RB) establishment or modification. A WTRU centric solution may be used for UL starvation avoidance in LTE and may be specified based on a number of token buckets. FIG. 1 shows an example token bucket configuration 100.
As shown in FIG. 1, tokens are added to each bucket in accordance with a certain rate, (e.g., tokens/section). In order to schedule and send a packet of size X tokens from the WTRU, the WTRU checks the current token bucket size to see if there are sufficient tokens to allow the sending of this packet, (i.e., if packet size<=token bucket size), and if so, the WTRU may send the packet. If there are not sufficient tokens to allow the sending of the packet, the WTRU will not send the packet at the present time, but may send it once a sufficient number of tokens have been accumulated.
There are, however, various issues when the WTRU centric solution is used for UL starvation avoidance in the LTE system. Since the relation between the buffer status reporting (BSR) and the configured MBR/GBR has not been addressed in RAN2, an impending grant loss problem may arise. If a grant loss occurs, signaling overhead, resource allocation loss, and the like may arise.
In general, grant loss refers to the WTRU receiving a grant but not being able to fully utilize it. Grant losses may occur since the WTRU does not know with what rate it will receive grants, making it difficult for the WTRU to determine upfront whether a certain buffer level will exceed the configured MBR/aggregate MBR (aMBR) when this buffer level is handled. So there is not currently a mechanism for the WTRU to take the configured MBR/aMBR into account when reporting the BSR. As a result, a situation might occur in which a WTRU reports a certain buffer level, but when it is obtaining UL grants for handling this buffer level, it is not allowed to schedule the concerning SAE bearer because that would mean crossing the configured MBR/aMBR. This is what may be referred to as a “grant loss”. The grant loss may occur even if an evolved Node B (eNB) is only providing grants corresponding to data indicated in the BSR.
It would therefore be beneficial to provide a method and apparatus for supporting UL starvation avoidance in an LTE system.